1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine or a printer, and more particularly to an image forming apparatus having a temperature detecting device for controlling an image forming condition.
2. Description of the Related Art
Hitherto, as the image forming apparatus of this type, there is known an image forming apparatus using the electrophotographic system such as a laser printer or a copying machine. Hereinafter, the image forming apparatus of the electrophotographic process will be described with reference to FIG. 12. FIG. 12 is a schematic cross-sectional view showing an image forming apparatus as background art.
A recording medium 102 set in a paper feed cassette 103a is transported to a transfer position by a pick-up roller 103b, a pair of feed and retard rollers 103c, a pair of conveying rollers 103d and a pair of conveying rollers 103e. A transfer roller 104 is located at the transfer position as a transferring means, and a toner image on a photosensitive drum 107 is transferred onto the recording medium 102 by applying a voltage thereto.
In this example, the photosensitive drum 107 is charged by a charging means 108, and then a laser beam is irradiated onto the photosensitive drum 107 from an optical means 101 to form a latent image corresponding to image information on the photosensitive drum 107. The latent image is developed by a developing means 109 into a visible image, that is, a toner image.
The recording medium 102 onto which the toner image has been transferred is conveyed to a fixing means 105 through a conveyance belt 103f. The fixing means 105 applies heat and pressure to the recording medium 102 that is passing through the fixing means 105, to thereby fix the transferred toner image onto the recording medium 102.
In particular, in the case where the fixing means 105 is of the film heating system (disclosed in Japanese Patent Application Nos. Sho 63-313282, Hei 2-157878, Hei 4-44075 to 44083, Hei 4-204980 to 204984, and so on), a structure is made in which a heat-resistant film (heat-resistant fixing film) which is a rotary member for heating is brought in close contact with a heating member by a rotary member for pressurizing (elastic roller) which is a pressure member.
A pressured contact nip portion is formed at a portion of the heat-resistant fixing film which is nipped between the heating member and the pressure member, and the recording medium 102 that bears an unfixed image is introduced between the heat-resistant fixing film and the pressure member at the pressure contact nip portion. Then, the recording medium 102 is conveyed together with the heat-resistant fixing film, and the unfixed image is subjected to heat from the heating member and to pressure from the pressure member, which are given through the heat-resistant fixing film, to thereby fix the unfixed image on the recording medium 102 as a permanent image.
Thereafter, the recording medium 102 is conveyed by a pair of discharge rollers 103g and a pair of discharge rollers 103h and then discharged to a discharge tray 106.
In this example, a thermistor (not shown) is disposed within the fixing means 105, and a temperature is adjusted on the basis of the detected temperature information to determine an appropriate fixing temperature. Also, appropriate transfer control is conducted on the basis of current or voltage information when the recording medium 102 is nipped or not nipped between the photosensitive drum 107 and the transfer roller 104.
In this way, there is applied a system in which feedback is effected on the basis of the information within the control unit since the recording medium 102 mainly reaches the control means such as the transfer roller 104 or the fixing means 105.
Also, a fan 110 is disposed on a side surface of an image forming apparatus so that outside air is taken in and supplied to an air path formed in the apparatus to suppress a rise of a temperature within the apparatus.
However, the above-mentioned apparatus suffers from the following problems.
When the above-mentioned image forming apparatus is liable to be influenced by a temperature environment where the image forming apparatus is used, an excess of quantity of heat or a lack of quantity of heat is liable to be caused. In particular, in the case where the fixing means is of the film heating system, a low heat capacity linear heating member is employed as the heating member, and a thin-film and low heat capacity material is employed as the film. As a result, although an electric power can be saved and a wait time can be reduced, the image forming apparatus is liable to be influenced by the temperature environment where the image forming apparatus is used, and the excess of quantity of heat or a lack of quantity of heat is liable to be caused.
In case of an excess of heat quantity, a part of toner image remains on the film side, resulting in the possibility of occurring an image failure where the toner is transferred onto the recording medium after the film has made a round. On the other hand, in the case of a lack of heat quantity, there is the possibility of occurring fixing failure.
In this way, when the temperature of the outside air cannot be detected with high response and accuracy, appropriate fixing temperature control that takes the temperature of the outside air into account cannot be conducted.
Also, in the case where transfer bias control is conducted, if the temperature of the outside air cannot be detected with high response and accuracy, appropriate transfer bias control that takes the temperature of the outside air into account cannot be conducted as with the fixing temperature control. This also leads to the fear of the image failure.
The present invention has been made under the above-mentioned circumstances, and therefore an object of the present invention is to provide an image forming apparatus which is capable of detecting the temperature of outside air with high precision, and is capable of controlling a setting of an image forming condition corresponding to the outside air temperature to improve its image quality.
Another object of the present invention is to provide an image forming apparatus comprising: an image forming means for forming an image on a recording material; a temperature sensor that detects a temperature; and an outside air take-in means for taking in and supplying outside air to the apparatus through an intake; wherein the condition of the image forming means is controlled on the basis of an output from the temperature sensor, and the temperature sensor is disposed in the vicinity of the intake.
Other objects of the present invention will become apparent from the following description.